Soviet 7000-series clones

The family of Soviet clones of Tektronix 7000-series scopes included models
S1-91, S1-115, S1-122 and S8-21 (Cyrillic: С1-91 etc.). They used the same plug-in modules, of which 14 types were available.

The base model S1-91 was introduced in 1977 and had 100 MHz bandwidth. It was "heavily inspired" by the Tektronix 7603.
(Compare also the Hungarian TR-4658.) Unlike the 7603, the S1-91 only has a 1 cm graticule size.

These scopes were designed at Vilnius Research and Development Institute of Radio Measuring Instruments (Lithuania).

However, they are not directly compatible with Tektronix plugins since mechanical parts and connectors use metric sizes.